The present invention relates to an air bag apparatus provided with a switch and a steering wheel.
Such prior art automobile steering wheels typically include a switching device such as a horn switch, which is incorporated in an air bag apparatus installed on a boss (the center pad portion).
For example a switching device may be installed on a boss of a steering wheel body, and the air bag apparatus as a whole is supported elastically to be capable of moving back and forth by means of the switching device. However, since the weight of the air bag apparatus as a whole is supported by a spring installed in the switching device, it is necessary to make the spring stiffer, thus giving rise to a problem of making it difficult to improve the feel of operating the switching device.
Japanese Laid-open Patent Publication No. 10-297390 discloses an air bag apparatus including an inflator, a base plate whereon the inflator is mounted, a horn switch base of cylindrical shape which is secured on the base plate, and a cover body that also serves as a horn button and is slidably mounted on the horn switch base. The switching device is installed in a sliding portion between the side wall of the cover body and the horn switch base.
In this prior art apparatus, the weight that must be supported by the switching device is reduced and the feeling of operation can be improved, although the air bag apparatus requires a separate horn switch base. The device becomes complicated because the switching device is incorporated in the side wall of the cover body. It therefore becomes difficult to reduce the manufacturing cost and to make the air bag apparatus compact, thereby making it difficult to design the steering wheel with an improved appearance.
The present invention has been made in view of the points described above, and an object thereof is to provide an air bag apparatus and a steering wheel of such a design to include a switch that has a simple constitution, can be made with a reduced manufacturing cost and can be made small in size.
The air bag apparatus of the present invention comprises an air bag, an inflator that supplies a gas to the air bag, a base portion of a base body that is attached to a steering wheel body and has the air bag and the inflator mounted thereon, the base body having a surrounding wall formed to protrude in a closed or substantially closed shape on the front side of the base portion, a cover body consisting of a lid that covers the front side of the surrounding wall and a side wall that is formed to protrude downwardly along said surrounding wall, preferably in a closed or substantially closed shape, on the back side of the lid and is located on the outer peripheral side of the surrounding wall, and a switching device that is located on the outer peripheral side of the side wall and is provided with an urging means for urging the cover body away from the base portion, a first contact supported on the back side of the lid, and a second contact which opposes the back side of the first contact and is supported by at least one of the base body and the steering wheel body.
In this constitution, when a force is not applied to the front side of the cover body, the cover body is urged by the urging means of the switching device so that the first contact is held at a position away from the second contact. When the lid of the cover body is pressed against the urging force of the urging means, the first contact is forced via the lid to move and make contact with the second contact thereby to close the contacts. Since the switching device supports only the cover body, not the entire air bag apparatus, the urging force of the urging means can be reduced and the feeling of operation of the switching device can be improved. Moreover, since the switching device is operated by pressing directly on the lid, the feeling of operation of the switching device can be improved compared to such a constitution wherein the entire air bag and the side wall of the cover body are provided between the pressing portion and the switching device. Also because the switching device is located on the outer peripheral side of the side wall of the cover body, constitution of the cover body and the base body is simplified, the manufacturing cost can be reduced and the apparatus can be reduced in size.
In the air bag apparatus, the height of the surrounding wall of the base body is substantially equal to the total height of an air bag housing portion enclosing the air bag.
The air bag enclosed in the air bag housing portion is protected from the cover body, that moves back and forth when the switching device is pressed to operate, by providing the surrounding wall of the base body with a height that is substantially equal to the total height of the air bag housing portion.
The air bag apparatus is provided with a wrapping, which covers at least a part of the front side of the air bag enclosed in the air bag housing portion.
In this constitution, the air bag that is incorporated in a folded up condition can be maintained in a desired shape and kept stationary at a desired position, while the air bag incorporated in the air bag housing portion is protected from the cover body that moves back and forth when the switching device is pressed to operate.
In the air bag apparatus, the surrounding wall of the base body is formed integrally with the base portion.
In this constitution, the constitution is simplified to have a reduced number of component parts, so that the assembly operation is also simplified. The manufacturing cost is reduced, and the apparatus is also smaller in size.
In the air bag apparatus, an engagement portion is provided on one of the surrounding wall and the side wall, and a lock receiving portion engaging with and holding the engagement portion movably within a predetermined range in back and forth directions is provided on the other of the surrounding wall and the side wall.
In this constitution, the constitution is simplified with a reduced number of component parts, so that the assembly operation is also simplified. The manufacturing cost is reduced, and the apparatus is also smaller in size.
In the air bag apparatus, the lock receiving portion guides the engagement portion freely in such a direction as the contacts make contact with and depart from each other in a range of movement caused by normal operation of the switching device.
In this constitution, the feeling of operation of the switching device can be improved since contact between the cover body and the base body is restricted and the distance between the contacts is regulated by the switching device only during operation of the switching device.
The base body can be molded as a single body using a die by forming the base portion, the surrounding peripheral wall that is formed to protrude in a closed or substantially closed shape on the front side of the base portion and a support portion that is provided on the outer peripheral portion of the surrounding peripheral wall to oppose the back side of the lid and support the second contact.
In this constitution, the base body of a complicated structure can be molded integrally in a predetermined die. Wall thicknesses required for any position can be arbitrarily set, thereby rationalizing and optimizing the structure, thus making it possible to achieve a proper strength while reducing the total weight. Moreover, the base body can be formed integrally in a single process, thus making it unnecessary to construct the base body from a number of separate parts, thereby realizing a structure having fewer or no joints, resulting in a simplified process of manufacturing the base body and reduced manufacturing cost. Also it becomes possible to use a material that is highly workable in a plastic state, without any tedious joining processes.
In the air bag apparatus, the switching device has a bracket that holds the first contact and supports at least the outer peripheral side of the side wall.
In this constitution, since at least the outer peripheral side of the side wall is supported by the bracket that holds the first contact, the side wall of the cover body can be restricted from deforming without making the construction complicated. Since the bracket is located on the outer peripheral side of the surrounding wall and the side wall, the operations of assembly and inspection are made easier.
The steering wheel of the present invention comprises the steering wheel body serving as a member to be mounted and consisting of a boss mounted on a steering shaft, a wheel for operation and spokes that connect the boss and the wheel. The air bag apparatus provided with the switching device is installed on the spoke.
In this constitution, since the air bag apparatus is provided with a switching device having a good feeling when operated that is located on the spokes, the air bag apparatus can be smaller in size and a steering wheel of an improved appearance can be provided.